This invention relates to a combinatorial weighing system and, more particularly, to a combinatorial weighing system wherein a combinatorial weighing operation can continue, without suspension, even if some of the weighing stations constituting the system malfunction.
A combinatorial weighing apparatus has a plurality of weighing machines each consisting of a weighing hopper and a weight sensor associated with the weighing hopper. According to a known combinatorial weighing method, combinatorial weighing is carried out by weighing articles which have been introduced into the weighing hoppers of the weighing machines, selecting the combination of weighing machines (referred to as the "optimum" combination) containing articles that give a total weight value equal to a target weight value or closest to the target weight value within preset allowable limits, discharging only those articles contained by the weighing hoppers of the selected weighing machines, and subsequently replenishing the emptied weighing hoppers with articles to prepare for the next weighing cycle. The foregoing sequence of steps is repeated to automatically carry out a continuous, highly accurate weighing operation.
FIGS. 1 and 2 are views useful in explaining a combinatorial weighing apparatus for practicing the foregoing weighing method, in which FIG. 1 is a schematic view of the weighing mechanism, and FIG. 2 is a block diagram of a combination control unit. Numeral 11 in FIG. 1 denotes a main feeder of vibratory conveyance type. Articles to be weighed are introduced into the main feeder 11 and imparted with vibratory motion for a predetermined length of time so as to be dispersed radially outward from the center of the main feeder. Each numeral 12 denotes n-number of weighing stations which are arranged around the main feeder 11 along radially extending lines to receive the articles dispersed by the main feeder. Each weighing station 12 includes a dispersing feeder 12a, a pool hopper 12b, a pool hopper gate 12c, a weighing hopper 12d, a weight sensor 12e, and a weighing hopper gate 12f. The dispersing feeder 12a comprises an independently vibrating conveyance device for feeding the articles by means of vibration, or an independently operable shutter arrangement. In either case, each dispersing feeder 12a is so arranged that an amount of articles received from the centrally located main feeder 11 can be introduced into the corresponding pool hopper 12b disposed therebelow. The pool hopper gate 12c is provided on each pool hopper 12b in such a manner that the articles received in the pool hopper 12b are released into the weighing hopper 12d when the pool hopper gate 12c is opened. Each weighing hopper 12d is provided with a weight sensor 12e of its own. The weight sensor 12e is operable to measure the weight of the articles introduced into the corresponding weighing hopper, and to apply an electrical signal indicative of the measured weight to the combination control unit shown in FIG. 2. The combination control unit then selects the combination of articles (the "optimum" combination) which gives a total weight closest to the target weight value, as will be described below in further detail. Each weighing hopper 12d is provided with its own weighing hopper gate 12f. A drive control unit, shown in FIG. 2, upon receiving the signals from each of the weight sensors, produces a signal to open only the weighing hopper gates 12f of those weighing hoppers 12d that give the optimum combination. The selected gates 12f discharge the articles from the corresponding weighing hoppers 12d into a common chute 13 where they are collected together. The collecting chute 13 has the shape of a funnel and is so arranged as to receive the articles from any of the circularly arrayed weighing hoppers 12d via the hopper gates 12f, which are located above the funnel substantially along its outer rim. The articles received by the collecting chute 13 are collected at the centrally located lower end thereof by falling under their own weight or by being forcibly shifted along the inclined wall of the funnel by a mechanical scraper or the like, which is not shown. The collecting chute 13 is provided with a timing hopper 14 at the lower end thereof for temporarily holding the collected articles. The arrival of an externally applied signal from a packaging machine or the like causes the timing hopper 14 to release the retained articles from the system.
Reference will now be made to the block diagram of FIG. 2 for a description of the combination control unit. Numeral 20 denotes the combination control unit which includes an n-bit (n=10) counter 21 for counting timing pulses TP of a predetermined frequency, and for generating all combinations of n-number of the weighing hoppers. These combinations will also be referred to as "combination patterns" where appropriate. Specifically, for n-number of weighing hoppers, n combinations are possible when each combination is composed of one weighing hopper from the total of n weighing hoppers, n(n-1)/2! combinations are possible when each combination is composed of two weighing hoppers selected from the total, and, in general, n(n-1)(n-2) . . . (n-r+1)/r! combinations are possible when each combination is composed of r-number of weighing hoppers selected from the total of n weighing hoppers. Accordingly, when the n-bit binary counter 21 has counted 2.sup.n -1 timing pulses TP, a total of 2.sup.n -1 different bit patterns, from 000 . . . 001 to 111 . . . 111, will have been generated. Therefore, if correlation is established between the first bit and the first weighing hopper, between the second bit and the second weighing hopper, and between third through n-th bits and the third through n-th weighing hoppers, then the generated bit pattern will be an indication of the abovementioned combination pattern.
A multiplexer 22, in accordance with the output bit pattern of the counter 21, provides an arithmetic unit 26 with read values (indicative of the weight of the article batches) from the weight sensors 12e of predetermined weighing hoppers. For instance, if the value of the count (the bit pattern) in counter 21 is 1000101011 when n=10, then the arithmetic unit 26 will receive the weight value outputs W1, W2, W3, W4, W6 and W10 from the weight sensors 12e attached to the first, second, fourth, sixth and tenth weighing hoppers, respectively. A target weight register 23, for storing a target weight value W.sub.a, is connected to the arithmetic unit 26 to apply W.sub.a thereto. Numerals 24 and 25 denote upper and lower limit setting devices, respectively, for storing preset allowable limits (namely an upper limit or maximum value Ma, and a lower limit or minimum value Mi, respectively) which are desirable for weight values. The minimum value Mi is set equal to the target weight value, as is customary. If it were set lower than the target weight value, the result could be delivery of articles having a total weight less than that intended, and complaints might ensue.
The arithmetic unit 26 computes and delivers a signal indicative of the total weight .SIGMA.Wi (=X) of the weight values received from the multiplexer 22, and also computes the difference between the total weight .SIGMA.Wi and the preset value Wa. The arithmetic unit 26 produces a signal A indicating the absolute value of the computed difference. More specifically, the arithmetic unit 26 performs the operations: EQU .SIGMA.Wi=X (1) EQU .vertline..SIGMA.Wi-Wa.vertline.=A (2)
and produces a signal representing the total weight .SIGMA.Wi (=X), as well as a signal A representing the absolute value (hereafter referred to simply as the "deviation") of the difference between the total weight .SIGMA.Wi and the preset value Wa. The value X is applied to a comparator 27, whose output is connected to a proper weight counter 28. The comparator 27 discriminates whether the total weight value X lies in the range defined by Mi and Ma. Specifically, if the following relation holds: EQU Mi.ltoreq.X.ltoreq.Ma (3)
then the comparator 27 will increment (count up) the counter 28 by one. A minimum deviation register 29 for storing the minimum deviation is set automatically to the deviation A the first time only, and thereafter is updated as the conditions warrant, as will be described later. In the case where the minimum value Mi is set equal to the preset value, it is permissible to initially set the minimum deviation register 29 to the difference between the maximum value Ma and the preset value. An optimum combination memory 30 is adapted to store the optimum combination pattern. Numerals 31 and 32 denote gates. When the total weight value .SIGMA.W.sub.i is within the preset allowable limits, a comparator 33 compares the deviation value A, namely the output of the arithmetic unit 26, with the prevailing minimum deviation value, denoted by B, stored in the minimum deviation register 29. When the inequality A&lt;B holds, the output of comparator 33 is such that the deviation value A is delivered for storage to the minimum deviation register 29 through the gate 31, and the content (combination pattern) of counter 21 is delivered for storage to the optimum combination memory 30.
When the state of counter 28 is one or more, a drive control unit 34, which receives a signal from memory 30 indicative of the optimum combination pattern, is operable to open the weighing hopper gates 12f (FIG. 1) specified by the optimum combination pattern, so that the corresponding weighing hoppers discharge their articles into the collecting chute 13, and to open the corresponding pool hopper gates 12c so that the emptied weighing hoppers 12d may be replenished with articles.
The operation of the weighing apparatus will now be described. At the beginning, each of the pool hoppers 12b and weighing hoppers 12d contains a supply of the articles. The weight sensors 12e provided on the corresponding weighing machines measure the weights of the articles within the respective weighing hoppers and produce the weight values W1 through W10 which are sent to the combination control unit 20. The n-bit (n=10) counter 21 counts the timing pulses TP having the predetermined frequency to produce 2.sup.n -1 combination patterns. Thus, when the first timing pulse TP arrives and is counted, the content of counter 21 becomes 0000000001. As a result, the multiplexer 22 sends the first weight value signal W1, from the weight sensor 12e provided on the first weighing hopper, to the arithmetic unit 26, which responds by performing the operation specified by Eqs. (1) and (2) above, thereby producing the total weight value .SIGMA.Wi of the combination, as well as the deviation A (=.vertline.W1-W.sub.a .vertline.) between the total weight value .SIGMA.Wi and the target weight value Wa. Since the gates 31 and 32 will be open for the initial combinatorial computation, the deviation value A is transferred to and stored in the minimum deviation register 29, and the content (the combination pattern 0000000001) of n-bit counter 21 is stored in the optimum combination memory 30. Comparator 27 compares the total weight .SIGMA.Wi (=X) against the maximum value Ma and the minimum value Mi, and increments the proper counter 28 when the relation M.sub.i .ltoreq.X.ltoreq.M.sub.a holds. Thenceforth, when the second timing pulse TP is generated, the pulse is counted by counter 21, whose state (combination pattern) is incremented to 0000000010. Consequently, the weight value output W2 of the weight sensor 12e provided on the second weighing hopper is delivered to the arithmetic unit 26 which then performs the operations of equations (1) and (2) to produce the signals indicative of the total weight .SIGMA.Wi (=X) and of the deviation value A (A=.vertline.W2-Wa.vertline.). The comparator 27 then determines whether relation (3) is satisfied; if it is, then the state of the proper weight counter 28 is incremented by one. The comparator 33, meanwhile, compares the deviation value A with the state B (=.vertline.W1-Wa.vertline.) of the minimum deviation register 29. If the relation A.gtoreq.B holds, then neither the register 29 nor the optimum combination memory 30 is updated; if A&lt;B holds, the deviation value A is transferred to and stored in register 29, and the state of counter 21 is transferred to and stored in the optimum combination memory 30. The operation described above is repeated until all 2.sup. n -1 combinations have been generated. At such time the content of the minimum deviation register 29 will be the minimum deviation value obtained from the 2.sup.n -1 combinations, and the content of the optimum combination memory 30 will be the combination pattern that gave the minimum value. The optimum combination is thus selected from the total of 2.sup.n -1 possible combination patterns.
If the value of the count in counter 28 is one or more, the drive control unit 34 opens the weighing hopper gates 12f of weighing machines corresponding to the "1" bits of the input combination pattern (namely the optimum combination pattern), whereby the articles in these weighing hoppers constituting the optimum combination are discharged into the collecting chute 13, after which the drive control unit 34 opens the corresponding pool hopper gates 12c to replenish the emptied weighing hoppers 12d with articles. Further, the dispersing feeders 12a corresponding to the emptied pool hoppers are vibrated for a fixed length of time to resupply these pool hoppers with articles.
This completes one combinatorial weighing cycle, which may be repeated as often as required, to provide batches of the articles, each batch having a total weight equal or closest to the preset value. It should be noted that when the state of the proper weight counter 28 is zero in the foregoing operation, articles are not discharged and each of the weighing machines must be supplemented with articles to resume the combinatorial computations.
With the above-described combinatorial weighing method, even articles which exhibit a great difference in weight from one to another can be weighed out to within an error that is less than the article unit weight, thereby making it possible to achieve a highly accurate weighing operation.
In an automatic weighing apparatus of the aforementioned combinatorial type in which combinations are formed among N weight values, 2.sup.N -1 combinations are obtained, as already described. It is known that satisfactory accuracy can be achieved if N is a value from seven to ten when weighing such articles as ordinary agricultural products, fishery products, industrial parts, foodstuffs and fabricated products.
The number of combinations necessary to obtain a desirable accuracy depends upon such factors as the required accuracy, the nature of the articles and the manner in which the articles are supplied. Depending on these factors, there are cases where an automatic weighing apparatus having, say, ten weighing stations can weigh out articles to a satisfactory accuracy even when some of the weighing stations are not used. In other words, there are situations where there is no marked decline in accuracy even if the number of combinations formed is reduced to approximately half, as would be the result if N were diminished by one. This means that if a certain weighing station were to develop a malfunction, weighing could, in certain circumstances, continue without using the faulty weighing station.
When a specific weighing station malfunctions, the prior-art practice is to issue an alarm and suspend the operation of the weighing machines. If the problem can be remedied without excessive delay, then the automatic weighing operation may be resumed following the necessary repairs. Where the problem is such that immediate repair is not possible, the operator manipulates a so-called "non-participation" switch to exclude the faulty weighing station from the weighing operation. Even if several of the weighing stations malfunction, therefore, the conventional method allows the weighing operation to be resumed without shutting down the weighing apparatus. Nevertheless, suspending the overall weighing operation, even temporarily, has an adverse effect of major proportions on the production line equipment preceding and following the weighing apparatus, and results in diminished weighing efficiency.
Accordingly, it has been contemplated to merely present some indication of weighing stations detected as having malfunctioned, while allowing weighing to proceed without any suspension in operation. However, a problem that arises with this technique is that the combinatorial weighing computations do not provide satisfactory results when the malfunctioning weighing stations grow large in number. In other words, an excessive number of combinations provide total weight values that fall outside the allowable limits, the end result being a weighing operation having poor accuracy.